Evolution of plasticized MnO–Al2O3–SiO2-based nonmetallic inclusion in 18wt%Cr-8wt% Ni stainless steel and its properties during soaking process

The properties of MnO–Al2O3–SiO2-based plasticized inclusion are likely to change during soaking process due to its low melting point. In this study, the evolution of the MnO–Al2O3–SiO2-based inclusion of 18 wt%Cr-8 wt%Ni stainless steel under isothermal soaking process at 1250°C for different times was investigated by laboratory-scale experiments and thermodynamic analysis. The results showed that the inclusion population density increased at the first stage and then decreased while their average size first decreased and then increased. In addition, almost no Cr2O3-concentrated regions existed within the inclusion before soaking, but more and more Cr2O3 precipitates were formed during soaking. Furthermore, the plasticity of the inclusion deteriorated due to a decrease in the amount of liquid phase and an increase in the high-melting-pointphase MnO–Cr2O3 spinel after the soaking process. In-situ observations by high-temperature confocal laser scanning microscopy(CLSM) confirmed that liquid phases were produced in the inclusions and the inclusions grew rather quickly during the soaking process. Both the experimental results and thermodynamic analysis conclude that there are three routes for inclusion evolution during the soaking process. In particular, Ostwald ripening plays an important role in the inclusion evolution, i.e., MnO–Al2O3–SiO2-based inclusions grow by absorbing the newly precipitated smaller-size MnO–Cr2O3 inclusions.

Corrosion properties of high silicon iron-based alloys in nitric acid

The effect of copper and rare-earth elements on corrosion behavior of high silicon iron-based alloys in nitric acid was studied by means of static and loading current corrosion experiments.The anodic polarization curve was also made to discuss the corrosion mechanism.The examination on alloy microstructure and SEM corrosion pattern showed that when silicon content reached 14.5%,the Fe3Si phase appeared and the primary structure of the iron-base alloy was ferrite.When adding 4.57% copper in the iron alloy,its corrosion resistance in static diluted sulfuric acid was improved while its corrosion resistance and electrochemical corrosion properties in the nitric acid were decreased.In contrast,the addition of rare earth elements could improve the corrosion properties in all above conditions including in static diluted sulfuric acid and in nitric acid.

Deformation Mechanism of Bimodal Structured 2205 Duplex Stainless Steel in Two Yield Stages

A kind of micro/nanostructured 2205 duplex stainless steel(DSS)with uniform distribution of nanocrystals was prepared via aluminothermic reaction method.The analysis of stress-strain curve showed that the fracture strength and elongation of the specimen were 946 MPa and 24.7%,respectively.At present,the research on microstructure of bimodal 2205 DSS at room temperature(RT)mainly depended on scanning electron microscope(SEM)observation after loading experiments.The test result indicates that there are two different yield stages in stress-strain curve of specimen during tensile process.The microstructure of duplex bimodal structured stainless steel consists of two pairs of soft hard regions and phases.By studying deformation mechanism of bimodal structured stainless steel,the interaction between soft phase and hard phase are discussed.The principle of composition design and microstructure control of typical duplex stainless steel is obtained,which provides an important research basis for designing of advanced duplex stainless steel.

Implementation Measures for Fire Work Safety in Gas Area of Metallurgical Enterprises

It is an important task to control the dangerous operation of gas fire and reduce the occurrence of gas fire and explosion accidents in ensuring gas operation safety in metallurgical enterprises.Combined with the require-ments of current laws,standards and practical experience,the key points in fire safety management and control are analyzed to solve the gas fire safety problems.

Characteristics of shell thickness in a slab continuous casting mold

The key to reduce shell breakout in the continuous casting process is to control shell thickness in the mold. A numerical simulation on the turbulent flow and heat transfer coupled with solidification in the slab mold using the volume of fluid （VOF） model and the enthalpy-porosity scheme was conducted and the emphasis was put upon the flow effect on the shell thickness profiles in longitudinal and transverse directions. The results show that the jet acts a stronger impingement on the shell of narrow face, which causes a zero-increase of shell thickness in a certain range near the impingement point. The thinnest shell on the slab cross-section locates primarily in the center of the narrow face, and secondly near the comer of the wide face. Nozzle optimization can obviously increase the shell thickness and make it more uniform.

Influence of refining process and utilization of different slags on inclusions, titanium yield and total oxygen content of Ti-stabilized 321 stainless steel

Ti-stabilized 321 stainless steel was prepared using an electric arc furnace, argon oxygen decarburization (AOD) furnace, ladle furnace (LF), and continuous casting processes. In addition, the effect of refining process and utilization of different slags on the evolution of inclusions, titanium yield, and oxygen content was systematically investigated by experimental and thermodynamic analysis. The results reveal that the total oxygen content (TO) and inclusion density decreased during the refining process. The spherical CaO–SiO2–Al2O3–MgO inclusions existed in the 321 stainless steel after the AOD process. Moreover, prior to the Ti addition, the spherical CaO–Al2O3–MgO–SiO2 inclusions were observed during LF refining pro-cess. However, Ti addition resulted in multilayer CaO–Al2O3–MgO–TiOx inclusions. Two different samples were prepared by conventional CaO–Al2O3-based slag (Heat-1) and -TiO2-rich CaO–Al2O3-based slag (Heat-2). The statistical analysis revealed that the density of inclusions and the -TiOx content in CaO–Al2O3–MgO–TiOx inclusions found in Heat-2 sample are much lower than those in the Heat-1 sample. Furthermore, the TO content and Ti yield during the LF refining process were controlled by using -TiO2-rich calcium aluminate synthetic slag. These results were consistent with the ion–molecule coexist-ence theory and FactSage?7.2 software calculations. When -TiO2-rich CaO–Al2O3-based slag was used, the -TiO2 activity of the slag increased, and the equilibrium oxygen content significantly decreased from the AOD to LF processes. Therefore, the higher -TiO2 activity of slag and lower equilibrium oxygen content suppressed the undesirable reactions between Ti and O.

Effect of microstructure variation on corrosion properties of as-cast 0Cr23Ni13 stainless steel at high strain rate of hot compression

The optimization of hot compression technique of as-cast 0Cr23Ni13 stainless steel at high strain rate was discussed,and its corrosion resistance was evaluated after hot compression treatment experimentally.By adjusting the dynamic recrys-tallization(DRX)ratio of 0Cr23Nil3 stainless steel during hot pressing,the content of low Σ coincident site lattice(ΣCSL)grain boundaries is increased,and the grain orientation is optimized.The results show that ferrite and austenite are completely recrystallized at 1050 and 1150℃,respectively.The number of grains in the<111>and<101>directions increases significantly,the corrosion potential increases,and the corrosion current density decreases,which will signifi-cantly improve the corrosion resistance of 0Cr23Nil3 stainless steel.After the optimization of grain boundary distribution,corrosion resistance is noticeably improved due to the existence of lowΣCSL boundaries.The interference effect of lowΣCSL grain boundary on random grain boundary network becomes intense with the increase in DRX ratio,which is the fundamental measure to improve the corrosion resistance.

In-situ observation and analysis of solidified structure evolution of S50C steel in soaking furnace

The evolution of solidified structure of S50C steel during heat treatment in compact strip production process was studied through an ultra-high-temperature confocal scanning laser microscope.It was found that the solidified structure consisted of dendritic crystals with secondary dendrite arm spacing ranging in 32-120μm,where carbon segregation was evident,and the dendrite arms wereα-Fe.The insignificant change was observed at a soaking temperature of 1180℃,whereas at 1300℃,the finer structure firstly disappeared,and then,the coarsening decreased,indicating that carbon tended to be homogenized.Therefore,the microsegregation was improved at 1300℃for 15 min.The phase transformation ofα-Fe→γ-Fe enhanced the carbon diffusion,and the evolution of the equivalent radius req was controlled by carbon diffusion.The diffusion coefficient of carbon(D=15μm2/s)was determined by using the inverse problem method.

Characteristics of Deoxidation and Desulfurization during LF Refining Al-killed Steel by Highly Basic and Low Oxidizing Slag

Steel and slag samples were taken at the start and the end of LF refining for steel plate cold common （SPCC）, in the compact strip production （CSP） process, and at the same time, the temperature and oxygen activity a[o] were measured by using an oxygen sensor. Furthermore, inclusions in steel samples were monitored by scanning electron microscopy （SEM） combined with energy dispersive spectroscopy （EDS）. It was confirmed that a [o] in liq- uid steel was in equilibrium with inclusion rather than with top slag during LF refining. Desulfurization was related to deoxidation since a[o] at slag-steel interface was clarified to be very close to that in liquid steel under the specific con- dition in LF with intense stirring by argon blowing and refined by highly basic low oxidizing slag for Al-killed steel. Sulfur partition ratio （Ls） was very sensitive to a[o]. Since a[o] increased rapidly with temperature rise, it not only offset promotion to desulfurization reaction with temperature rise but decreased Ls. For Al-killed steel, the.modifica- tion of Al2O3 for lowering the activity of Al2O3 in inclusion was believed to be favorable for both deoxidation and desulfurization during LF refining.

Effect of microstructure evolution on Luders strain and tensile properties in an intercritical annealing medium-Mn steel

The influence of microstructural characteristics on Lu¨ders strain and mechanical properties was explored by means of altering thermo-mechanical circumstances in an intercritical annealing(IA)medium-Mn Fe-11Mn-0.09C-0.25Si(wt.%)steel.By IA of cold-rolled samples with severe plastic deformation,exclusively equiaxed dual phases were obtained because of active recovery and recrystallization.The equiaxed austenite(gamma E)with a larger size and inadequate chemical concentration was more readily transformed into martensite,and subsequent transformation-induced plasticity(TRIP)effect was triggered actively at relatively higher IA temperature,lessening localized deformation.In addition,grown-in dislocations were prone to multiply and migrate around a broad mean free path for coarser equiaxed ferrite(alpha E)due to weakening dynamic recovery;therefore,it was the ensuing increased mobility of dislocations instead of reserving plentiful initial dislocation density that facilitated the propagation velocity of Luders bands and the accumulation of work hardening.In contrast,the bimodal-grained microstructure with lath-like and equiaxed austenite(gamma L+gamma E)satisfactorily contributed to a smaller yield point elongation(YPE)without compromise of comprehensive mechanical properties on the grounds that austenitic gradient stability gave rise to discontinuous but sustainable TRIP effect and incremental work hardening.Hence,Luders strain is closely related to the absence of work hardening in the region which yields locally.It follows that the decreased stability of retained austenite,favorable mobility of dislocations and the bimodal-grained structure all prominently make up for the insufficiency of work hardening,thereof resulting in a limited YPE.

Achieving strength-ductility synergy in novel paramagnetic Fe-based medium-entropy alloys through deep cryogenic deformation

Cryogenic pre-deformation treatment has been widely used to effectively improve the comprehensive mechanical properties of steels and novel metals.However,the dislocation evolution and phase transformation induced by different degrees of deep cryogenic deformation are not yet fully elucidated.In this study,the effects of multiple cryogenic pre-treatments on the mechanical properties and deformation mechanisms of a paramagnetic Fe_(63.3)Mn_(14-)Si_(9.1)Cr_(9.8)C_(3.8)medium-entropy alloy(MEA)were investigated,leading to the discovery of a pretreated MEA that exhibits exceptional mechanical properties,including a fracture strength of 3.0 GPa,plastic strain of 26.1%and work-hardening index of 0.57.In addition,X-ray diffraction(XRD)and transmission electron microscopy(TEM)analyses revealed that multiple cryogenic pre-deformation treatments significantly increased the dislocation density of the MEA(from 9×10^(15)to 4×10^(16)m^(-2)after three pretreatments),along with a transition in the dislocation type from predominantly edge dislocations to mixed dislocations(including screw-and edge-type dislocations).Notably,this pretreated MEA retained its paramagnetic properties(μ_(r)<1.0200)even after fracture.Thermodynamic calculations showed that cryogenic pretreatment can significantly reduce the stacking fault energy of the MEA by a factor of approximately four(i.e.,from 9.7 to2.6 m J·m^(-2)),thereby activating the synergistic effects of transformation-induced plasticity,twinning-induced plasticity and dislocation strengthening mechanisms.These synergistic effects lead to simultaneous strength and ductility enhancement of the MEA.

Effect of Cu on Surface Microcrack of Austenitic Stainless Cold Rolled Coil

In order to find out the cause of surface microcrack on 304 austenitic stainless cold rolled coils which is produced in a steel plant of China, lots of studies have been carried out. The results indicated that the copper guide of steekle mill used in hot rolling process contacts directly with the hot rolled coil, so parts of copper melt and glued to the surface of the stainless steel plates due to a higher temperature of stainless steel plates than the copper melting temperature, which leads to deterioration of austenitic grain boundaries. Shear stress produced in the process of repeatrolling on finishing mill induces the surface microcracks and promotes it. After changing the copper guide to the cast steel one, such kinds of surface microcracks have never appeared.